Extended nip press

ABSTRACT

An extended nip press for removing water from a traveling web in a paper machine including a press roll with an elongate shoe having a concave surface facing the roll and forming an extended nip therebetween with an endless belt trained over the shoe for passing through the nip and first and second belts passing through the nip with the belt supported by a plurality of guide rolls or by an annular shell having continuous smooth outer surface extending from the outgoing side of the nip back to the oncoming side of the nip with a beam within the shell and a uniform fluid support for the shoe supported on the beam.

This is a continuation of Ser. No. 403,122 filed July 29, 1982, nowabandoned; Reissue of 4,287,021, issued Sept. 9, 1981..Iaddend.

BACKGROUND OF THE INVENTION

The present invention relates to improvements in presses formechanically pressing water from a traveling web in a paper machine andmore particularly to a press of the type knwon as an extended nip presswherein the length of a single nip in the machine direction extendssubstantially longer than a nip of a conventional type formed betweentwo mating rolls.

Extended nip presses of this type have been formed in variousarrangements with one type of arrangement employing a roll as one of themembers of the press with a shoe supporting an endless traveling beltforming the other member of the press. A structure of this type is shownin the Justus U.S. Pat. No. 3,783,097. Difficulties have beenencountered in controlling and guiding the belt in this type ofarrangement and the present invention contemplates an arrangementwhereby problems encountered in structures heretofore available areavoided.

Accordingly, an object of the present invention is to provide animproved extended nip press of the type described with an arrangementfor supporting and guiding the belt whereby the path of travel of thebelt remains under control without deviation at high speeds required forpressing a traveling web in a paper making machine.

A further object of the invention is to provide an improved belt andsupport therefor in an extended nip press of the type described. Afurther object of the invention is to provide an extended nip pressusing an endless belt running through the nip wherein a structure isprovided that attains longer belt life and requires the belt to runthrough a less tortuous path than with structures heretofore availableand wherein the belt can operate at zero tension.

Other objects, advantages and features, as well as equivalent methodsand structures which are intended to be covered herein, will become moreapparent with the teaching of the principles of the invention inconnection with the disclosure of the preferred embodiment thereof inthe specification, claims and drawings, in which:

DRAWINGS

FIG. 1 is a vertical sectional view illustrating somewhat schematicallyan extended press constructed and operating in accordance with theprinciples of the present invention;

FIG. 2 is a sectional view taken substantially along line II--II of FIG.1 with the section being fragmentary; and

FIG. 3 is a view of a portion of the inside of the belt illustrating theoil transfer grooves therein.

DESCRIPTION

As shown in FIGS. 1 and 2, the press mechanism includes a roll 10 whichis preferably in the form of a hollow roll shell supported therein by asliding slipper bearing or shoe 13.

An opposing press shoe 11 having a concave upper surface 18 to conformto the outer surface of the roll shell forms a nip N therewith.

The hollow roll shell has the limber sliding shoe 13 therein which ispreferably of one piece and extends for the length of the roll shell,although it may be divided into adjacent sections. The shoe 13 ispivotally supported on a roll pin 14 which is supported on a piston 15positioned in an oil pressure channel 17 in a beam extending through theroll shell. The channel is pressurized beneath the shoe by suitable oilsupply means, not shown, and the piston 15 supports the limber shoe 13with a uniform pressure throughout its length so as to obtain uniformpressure throughout the length of the nip N.

Passing through the nip N is a first upper felt 23 and a second lowerfelt 24, and the web W is carried between the felts through the nip, mayenter the nip carried on the surface of one of the felts. The nip willextend essentially for the length of the shoe 11 which will subject theweb to a pressing pressure from the time it enters the oncoming side ofthe nip at 11a until it leaves on the offrunning side of the nip 11b.The shoe has a relieved lead-in or nose portion so as to receive a filmof lubricant provided by a lubricant supply nozzle 32 to lubricate theupper surface of the shoe and permit continuous sliding movement of anendless circular belt 25 along the shoe. The belt is formed of a heavyrubber of reinforced rubber.

As a feature of the present invention, the belt is run, not undertension, but free of tension and is guided in a natural circular path toleave and re-enter the nip. To define a natural circular path, a hollowtube or guide shell 26 is provided within the belt extending to supportthe belt and has an outer smooth surface 27. The surface extends from acircumferential location 33 immediately following the offrunning side ofthe nip to a location 30 immediately in advance of the oncoming side ofthe nip. The smooth outer surface of the guide shell 26 is preferablyprovided with oil relief holes 38 on the offrunning side to permit thedrainage of lubricant from beneath the surface of the belt. The oilwhich passes through the openings 38 is drawn off from a compartment 40beneath the passages.

The shell which supports the belt is of a diameter less than the belt soas to provide a free space 28 between the belt and the outer smoothsurface of the shell so that the belt travels under zero tension.Actually, preferably there is a small gap between the circular guideshell 26 and the belt.

Within the belt is a supporting framework 36 for the shell and theframework provides the oil return chamber 40 on the off-running side andan oil return chamber 41 on the oncoming side. Oil drain openings suchas 34 and 35 are provided from the compartment between the shoe toaccommodate the escape of oil into the oil return chambers 40 and 41.

Within the framework 36 and the looped belt 25 is a beam 21 extendingparallel to the nip. This beam is provided with a channel 22 with apiston 20 therein. The piston supports the shoe 18 on a roll pin 19 andthe channel 22 beneath the piston is supplied with a pressurized oilsimilar to the channel 17 and at a pressure essentially equal thereto.

On the offrunning side of the nip a doctor 29 aids in separating the oilfrom the inner surface of the belt.

For aiding in lubricating the belt and preventing the escape of oilaxially outwardly of the belt, the belt is provided with grooves on itsinner surface as shown by the grooves 42 in the surface 43 of the beltin FIG. 3. This tends to work the lubricant toward the center of thebelt, the grooves are relatively shallow as to not weaken the belt, andpreferably are in a spiral pattern with the spiral extending toward thecenter relative to the direction of travel of the inner surface of thebelt.

A belt cover 37 may be positioned outside of the belt to prevent it fromfluttering against its supporting surface and aid in guiding it. Inaddition to the elongate belt cover shown at 37, axially extending rodsmay be provided adjacent the outer belt surface to aid it in its stabletravel.

In operation, the hydraulic loading means in the channel 17 for the shoesupporting the roll shell 10 and the channel 22 beneath the pistonsupporting the shoe 11 are similarly pressurized and the web W travelsthrough the nip between the felts 23 and 24. The web enters the nip at11a and leaves at 11b for an extended travel under the pressure imposedwithin the nip which pressure is controlled by the pressure beneath thepistons in the chamber 17 and 22. The water is expressed into the feltand suitable felt drying means are provided for the looped felts 23 and24. In some instances, the outer surface of the roll 10 may be groovedto aid in the receipt of water by the felt 23 and the outer surface ofthe belt 25 may similarly be grooved to aid in the passage of the waterfrom the web into the felt 24.

The improved stable travel of the belt improves the quality of the paperweb being pressed in the nip. With structures heretofore used, improperalignment of the belt can affect the tension in the nip or createstresses on the felt and the web so that uniform pressing is disturbed.Further, by prolonging the working life of the belt, its satisfactoryoperation is prolonged and often failure of the belt could begin withoutbeing noticed by the paper machine operator, and defects in the weboccur before the machine could be shut down and the belt replaced. Thebelt is subjected to very hard wear and very high stresses by continualtravel through the press and the relaxation of the belt to its free formas it travels around the circular guide in the present form of theinvention, substantially improves performance and operation.

We claim as our invention:
 1. An extended nip press for removing waterfrom a traveling web in a paper machine comprising in combination:apress roll; an elongate shoe forming a press nip with said press rolland having a concave surface to conform to said roll so that the pressnip is formed elongate in the direction of web travel through the nip;.[.a first endless felt trained over said roll to travel through saidnip;.]. an endless belt trained over said shoe for passing through saidnip; .[.a second endless felt trained over said belt to travel throughsaid nip with the web passing through the nip between said felts;.]..Iadd.means for receiving water pressed from the web in said pressnip;.Iaddend. means for providing a lubricant between said shoe andbelt; and guide means within said belt guiding and supporting the belton the shoe;said guide means having an outer smooth curved surface of acircumference slightly smaller than the belt to provide a continualsmooth sliding surface for the belt so that the belt .[.operates underzero tension and.]. is self-aligning wherein the belt is guided.[.substantially.]. along .Iadd.substantially .Iaddend.the entirecircumference of the guide means.
 2. An extended nip press for removingwater from a traveling web in a paper machine constructed in accordancewith claim 1:wherein said press roll is a hollow roll shell with a beamextended therethrough; a sliding slipper bearing shoe means within theroll shell positioned opposite the nip for supporting the roll shell;and a fluid pressure support between the beam and shoe applying auniform supporting force to the shoe along the length of the roll.
 3. Anextended nip press for removing water from a traveling web in a papermachine constructed in accordance with claim 1.including a beamextending along within said belt parallel to the nip; and a fluidpressure support between the beam and said shoe applying a uniformsupporting force to the shoe along its length opposite the nip.
 4. Anextended nip press for removing water from a traveling web in a papermachine constructed in accordance with claim 1:wherein said surface isarranged to provide a space therein with a beam extending through saidspace and supporting said shoe.
 5. An extended nip press for removingwater from a traveling web in a paper machine constructed in accordancewith claim 1:including a plurality of openings in said outer smoothsurface located on the outgoing side of the nip.
 6. An extended nippress for removing water from a traveling web in a paper machineconstructed in accordance with claim 1:wherein said belt guide means hasa diameter slightly less than the diameter of said belt so as toaccommodate a radial space between the inner surface of the belt and theouter surface of the guide means.
 7. In an extended nip press forremoving water from a traveling web in a paper machine constructed inaccordance with claim 1:including means defining grooves on the insideof the belt with the grooves spiralling toward the center of the belt tomove lubricant axially inwardly along the belt. .Iadd.
 8. An extendednip press for removing water from water from a traveling web in a papermachine constructed in accordance with claim 1:wherein the belt operatesunder zero tension..Iaddend.